There has been known a waste water treatment device in which, in order to treat organic substances in waste water by degradation, a cathode nozzle covered entirely with an insulator except the exposed tip to serve as a first electrode and an anode opposed to the cathode nozzle to serve as a second electrode are disposed inside a treatment tank, and the first electrode and the second electrode are each connected to a high-voltage pulse power supply. In this type of waste water treatment device, bubbles are generated in waste water from the tip of the cathode nozzle while high-voltage pulses are applied to the cathode nozzle and the anode which are electrodes, thereby applying an electric field directly to the bubbles and causing “bubble electric discharge”. Bubble electric discharge generates oxidized radicals, with which organic substances in waste water are treated by degradation (see, for example, Patent Literature 1).
Causing bubble electric discharge requires supplying initial electrons. A problem is that the lack of free electrons in bubbles in water is not conducive to discharge. As a way to supply initial electrons necessary to start discharge to the interior of bubbles, hitherto, there has been known discharge-inside-bubbles that uses an X-ray irradiator to apply voltage while irradiating the space between opposed electrodes with an X-ray beam (see, for example, Non Patent Literature 1).